Apparatus for momentarily heating the surface of a mold

ABSTRACT

Disclosed herein is a system for momentarily heating the surface of a mold and system thereof. The system comprises a casting material feeder, upper and lower molds, an injection molding control, an air and gaseous fuel mixture and supply unit, an interface and a control panel. The casting material feeder serves to supply molten casting material. The upper and lower molds serve to form a predetermined shaped cast. The injection molding control serves to control the upper mold and the lower mold. The air and gaseous fuel mixture and supply, unit serves to supply compressed air and gaseous fuel simultaneously or selectively. The gaseous fuel mixture and supply control serves to control the operation of the air and gaseous fuel mixture and supply unit. The interface serves to interface the injection molding control and the gaseous fuel mixture and supply control. The control panel serves to visually display the control, condition and operation of the components of the system.

This a divisional of application No. 09/694,409, filed Oct. 23, 2000,now U.S. Pat. No. 6,544,024.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods for momentarilyheating the surface of a mold and system thereof, and particularly to amethod for momentarily heating the surface of a mold and system thereof,which is capable of momentarily heating the surface of the mold prior toinjection molding and cooling a molded product immediately after themolding, thereby improving the quality of products in appearance,preserving the physical and thermal properties of resin in the products,and increasing the productivity of a manufacturing process of theproducts for the reduction of the manufacturing cost of the products.

2. Description of the Prior Art

In a technical field where resin (such as synthetic resin, plastics orthe like) products are manufactured, various attempts have been made tomomentarily heat a mold to the same temperature as that of resin whilethe cavity of the mold is being filled with the resin, and to rapidlycool the mold after the cavity of the mold is filled with the resin. Theobject of these attempts is to increase the quality of products inappearance, to improve the strength and thermal properties of theproducts and to increase the productivity of the manufacturing processof the products for the reduction of the manufacturing costs of theproducts.

German Pat. Appln. No. 297 08 721.5 and PCT Appln. No. WO 98/51460disclose a mold capable of being temporarily heated by the flame ofgaseous fuel and synthetic resin forming method thereof. According tothe above described patents, a synthetic resin injecting mold process isautomated and the molded products of synthetic resin may is manufacturedcontinuously.

However, according to the above-described patents, since a moldedproduct cannot be cooled immediately after the forming of the product,the quality of the molded product is reduced in appearance, the strengthand thermal properties of the injection-molded product are deterioratedand the productivity of the molding process is reduced.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a method for momentarily heating the surface ofa mold, which allows the mold to be filled with molten resin forinjection molding after the preheating of the mold to a predeterminedtemperature and allows an injection-molded product to be cooled upon thecompletion of the injection molding, thereby increasing the quality ofthe injection-molded product in appearance and improving the strengthand thermal properties of the injection-molded product.

Another object of the present invention is to provide a system formomentarily heating the surface of a mold, which comprises upper andlower molds for forming resin and performing the heating of the upperand lower molds, a supply unit for supplying air and gaseous fuel, asafety unit for preventing the danger of gas explosion, and a controlunit for controlling the operation of the above components.

A further object of the present invention is to provide a method formomentarily heating the surface of a mold and system thereof, in whichone or more cores are disposed between its upper and lower molds, thecores are momentarily heated using gaseous fuel or an induction heater,and heating and cooling are performed in the process of injectionmolding, thereby improving the quality of an injection-molded product.

In order to accomplish the above object, the present invention providesa method for momentarily heating a surface of a mold, comprising thesteps of: opening upper and lower molds of the mold, and supplyinggaseous fuel; injecting and igniting the gaseous fuel from the lowermold after allowing the upper and lower molds to come close to eachother at a predetermined distance; heating the upper mold for apredetermined time period; filling a forming space between the upper andlower molds with molten material through the upper mold immediatelyafter stopping heating and closing the upper and lower molds; cooling amolded product by injecting compressed air to the molded product afterallowing the upper and lower molds to be opened at a predetermineddistance; and ejecting the molded product from the upper and lower moldsafter allowing the upper and lower molds to be completely opened.

In addition, the present invention provides a system for momentarilyheating the surface of a mold, comprising: a casting material feeder forsupplying molten casting material; upper and lower molds for forming apredetermined shaped cast; an injection molding control for controllingthe upper mold and the lower mold; an air and gaseous fuel mixture andsupply unit for supplying compressed air and gaseous fuel simultaneouslyor selectively; a gaseous fuel mixture and supply control forcontrolling the operation of the air and gaseous fuel mixture and supplyunit; an interface for interfacing the injection molding control and thegaseous fuel mixture and supply control; and a control panel forvisually displaying the control, condition and operation of thecomponents of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram showing a system for momentarily heatingthe surface of a mold using the flame of gaseous fuel in accordance withthe present invention;

FIG. 2 is a diagram showing piping for supplying air and gaseous fuel tothe main body of the system in detail;

FIGS. 3a to 3 f are process charts showing the method for temporarilyheating the surface of a mold using the frame of gaseous fuel inaccordance with an embodiment of the present invention;

FIGS. 4a to 4 d are process charts showing the method for temporarilyheating the surface of a mold using the frame of gaseous fuel inaccordance with another embodiment of the present invention;

FIGS. 5a to 5 d are process charts showing the method for temporarilyheating the surface of a mold using the frame of gaseous fuel inaccordance with a further embodiment of the present invention;

FIG. 6 is a block diagram illustrating the control panel of the systemfor momentarily heating the surface of a mold;

FIG. 7 is a schematic diagram showing a system for momentarily heatingthe surface of a mold using an induction heater in accordance with thepresent invention; and

FIG. 8 is a flowchart showing the operation of the system formomentarily heating the surface of a mold using the induction heater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now should be made to the drawings, in which the samereference numerals are used throughout the different drawings todesignate the same or similar components.

FIG. 1 is a schematic diagram showing a system for momentarily heatingthe surface of a mold using the flame of gaseous fuel in accordance withthe present invention. FIG. 2 is a diagram showing piping for supplyingair and gaseous fuel to the main body of the system in detail.

Reference numeral 10 designates a casting material feeder for supplyingmolten casting material. The casting material feeder 10 suppliesinjectable material, such as synthetic resin or metal.

An upper mold 20 is fixed to the lower end of the casting materialfeeder 10 under the casting material feeder 10. The upper mold 20 has acasting material supply hole 22 for supplying casting material from thecasting material feeder 10 to the upper mold 20, a cavity 24 for formingthe casting material into a predetermined-shaped cast. The upper mold 20is provided with a limit switch 83 for sensing the position of the uppermold 20.

A lower mold 30 is disposed under the upper mold 20. The lower mold 30comprises a mold portion 32 for insertion into the cavity 24 of theupper mold 20 to form the casting material into a predetermined-shapedcast, a lower mold supply conduit 31 formed in the lower mold 30 tosupply mixed gaseous fuel and compressed air, a plurality of dischargeholes 34 for heating and cooling the upper mold 20 using the mixedgaseous fuel and the compressed air supplied through the lower moldsupply conduit 31, an ignition unit 40 for igniting gaseous fuelinjected by an igniter 41 using high voltage current generated by a highvoltage generator 44 and sensing gaseous fuel flame by means of a flamesensor 42, a limit switch 84 for sensing the position of the lower mold30, an air and gaseous fuel mixture and supply unit 90 for supplying airor mixed gaseous fuel supplied through an air and mixed gaseous fuelsupply conduit 86, and an elevating cylinder 80 including an elevatingshaft 82 for selectively lifting or lowering the lower mold 30 by thecontrol of an injection molding control 50. The discharge holes 34 areconstructed in the form of slits, respectively have widths of 0.01 to0.1 mm, and are distributed on the surface of the lower mold 30 inaccordance with the shape of the cast.

Although not depicted in the drawing, conduits for supplying air andgaseous fuel and a coolant supply conduit for supplying coolant areprovided in the lower mold 30.

The upper and lower molds 20 and 30 are separately formed. The uppermold 20 and/or the lower mold 30 may be provided with additional partsnecessary for injection molding.

The injection molding control 50 controls the upper and lower molds 20and 30. In detail, the injection molding control 50 controls themechanical operation for an injection molding process.

The air and gaseous fuel mixture and supply unit 90 serves to supplycompressed air and gaseous fuel simultaneously or selectively, andcomprises a variety of pipelines for supplying air and/or gaseous fueland a variety of valves and gauges for controlling the flow of airand/or gaseous fuel. The air and gaseous fuel mixture and supply unit 90is divided into an air and gaseous fuel supply line 91 for ignition andan air and gaseous fuel supply line 110 for heating. A compressed airsupply line 130 for supplying compressed air and a gaseous fuel supplyline 140 for supplying gaseous fuel are respectively connected to theair and gaseous fuel mixture and supply unit 90. A compressed air supplysource 136 for supplying compressed air and a gaseous fuel supply source146 for supplying gaseous fuel are respectively connected to thecompressed air supply line 130 and the gaseous fuel supply line 140.

The air and gaseous fuel supply line 91 for ignition includes an air andgaseous fuel mixture element 92 for ignition, an air supply line forignition and a gaseous fuel supply line for ignition. The air supplyline for ignition includes a first pneumatic pressure gauge 93 formeasuring the pressure of supplied air, a first needle valve 94 forpreventing compressed air from flowing backward, and a first solenoidvalve 95 for interrupting the supply of compressed air and a firstmanual valve 96 for regulating the amount of supplied compressed air.The gaseous fuel supply line for ignition includes a first fluidicpressure gauge 101 for measuring the pressure of supplied gaseous fuel,a second needle valve 102 for preventing gaseous fuel from flowingbackward, and a second solenoid valve 103 for interrupting the supply ofgaseous fuel and a second manual valve 104 for regulating the amount ofsupplied gaseous fuel. The air and gaseous fuel mixture element 92 forignition serves to mix air and gaseous fuel supplied through the air andgaseous fuel supply lines for ignition.

The air and gaseous fuel supply line 110 for heating includes an air andgaseous fuel mixture element 111 for heating, an air supply line forheating, and a gaseous fuel supply line for heating. The air supply linefor heating includes a second pneumatic pressure gauge 112 for measuringthe pressure of supplied air, a third needle valve 113 for preventingcompressed air from flowing backward, and a third solenoid valve 114 forinterrupting the supply of compressed air and a first pressure switch115 for sensing the pressure of supplied compressed air and interruptingthe supply of compressed air when the pressure of the suppliedcompressed air is not equal to a predetermined value. The gaseous fuelsupply line for heating includes a second fluidic pressure gauge 120 formeasuring the pressure of supplied gaseous fuel, a fourth needle valve121 for preventing gaseous fuel from flowing backward, and a fourthsolenoid valve 122 for interrupting the supply of gaseous fuel and asecond pressure switch 123 for sensing the pressure of suppliedcompressed air and interrupting the supply of gaseous fuel when thepressure of the supplied gaseous fuel is not equal to a predeterminedvalue. The air and gaseous fuel mixture element 111 for heating servesto mix air and gaseous fuel supplied through the air and gaseous fuelsupply lines for heating.

The compressed air supply line 130 is connected to both air supply linefor ignition of the air and gaseous fuel supply line 91 for ignition andthe air supply line for heating of the air and gaseous fuel supply line110 for heating, while the gaseous fuel supply line 140 is connected toboth gaseous fuel supply line for ignition of the air and gaseous fuelsupply line 91 for ignition and the gaseous fuel supply line for heatingof the air and gaseous fuel supply line 110 for heating.

The compressed air supply line 130 serves to supply compressed airgenerated in and supplied from a compressed air supply 136, and thegaseous fuel line 140 serves to supply gaseous fuel supplied from thegaseous fuel supply source 146.

The compressed air supply line 130 comprises a first flux regulator 131for manually regulating the amount of compressed air, a first filter 132for filtering impurities included in compressed air, a fifth solenoidvalve 133 for interrupting the supply of compressed air, a thirdpneumatic pressure gauge 134 for sensing the pressure of suppliedcompressed air and a fifth manual valve 135 for regulating the amount ofsupplied compressed air. The fuel gas supply line 140 comprises a secondflux regulator 141 for manually regulating the amount of gaseous fuel, asecond filter 142 for filtering impurities included in gaseous fuel, asixth solenoid valve 143 for interrupting the supply of gaseous fuel, afourth pneumatic pressure gauge 144 for sensing the pressure of suppliedgaseous fuel and a sixth manual valve 145 for regulating the amount ofsupplied gaseous fuel.

A gaseous fuel mixture and supply control 70 serves to control theoperation of the air and gaseous fuel mixture and supply unit 90. Thegaseous fuel mixture and supply control 70 is connected to the injectionmolding control 50 through an interface 60, and receives signals fromand transmits signals to the injection molding control 50. The gaseousfuel mixture and supply control 70 includes a microprocessor.

In addition, there may be included a safety unit that serves toautomatically interrupt the supply of air and gaseous fuel when flamesare not sensed by the flame sensor 42 in a predetermined time periodafter ignition is performed by the igniter 41 of the ignition unit 40,gas of a predetermined degree of density is detected by a gas detector(not shown) disposed near the upper and lower molds 20 and 30, or thepressures of air and gaseous fuel inputted from a first pressure switch115 and a second pressure switch 123 are higher than a predeterminedpressure.

The heating system of the present invention includes a control panel forcontrolling the components of the system and inputting the operationalconditions of the components. The control panel is illustrated as ablock diagram in FIG. 6.

The control panel includes a key input unit 151, a sensing unit 152, aCentral Processing Unit (CPU) 153, an alarm 154, a display 155 and aninstrument panel 156.

The key input unit 151 has a plurality of keys, and serves to inputvarious operational conditions for injection molding.

The sensing unit 152 serves to sense the various states of the system,convert a sensing signal to an electric signal and output the electricsignal. The states include the elevation of the dies, the pressures andamounts of air and gaseous fuel, the leakage of gas and the like.

The CPU 153 serves to perform determination on the basis on an inputsignal and to output a control signal. The CPU 153 can be included inthe injection molding control 50 and the gaseous fuel mixture and supplycontrol 70.

The alarm 154 serves to warn of system error and danger situations. Thealarm 154 may be activated when gas leaks or pressure variations outsidepredetermined limits occur.

The display 155 serves to indicate the information of the operation ofthe system. A user can monitor the operation of the system using thedisplay 155.

The instrument panel 156 serves to indicate the operation of variouscomponents of the system. The instrument panel 156 may indicate thepressures of air and gaseous fuel and the state of safety.

Hereinafter, a method for momentarily heating the surface of a moldusing the flame of gaseous fuel is described with reference to FIGS. 3ato 3 f.

In STEP S100, the upper mold 20 and the lower mold 30 are opened at apredetermined distance and the supply of gaseous fuel is prepared.

In STEP S101, the upper mold 20 comes close to the lower mold 30 andgaseous fuel is injected and ignited. In more detail, compressed air andgaseous fuel are supplied from the compressed air supply source 136 andthe gaseous fuel supply source 146 through the compressed air supplyline 130 and the gaseous fuel supply line 140, enter the air and gaseousfuel supply line 91 for ignition and are mixed together while passingthrough the air and gaseous fuel mixture element 92, and the mixed airand gaseous fuel passes through the supply conduit 31 of the lower mold30, is injected through the discharge holes 34 of the mold portion 32and is ignited in the igniter 41 of the ignition unit 40 using highvoltage current generated in the high voltage generator 44. If flame isnot sensed by the flame sensor 42 after the ignition is performed, thesupply of air and gaseous fuel is interrupted by the operation of thesolenoid valves 95 and 103.

After the air and gaseous fuel supplied through and mixed in the air andgaseous fuel supply line 91 for ignition are normally injected,compressed air and gaseous fuel are supplied through and mixed in theair and gaseous fuel supply line 110 and are injected through the lowermold 30. At this time, the supply of the compressed air and gaseous fuelbeing supplied through the air and gaseous fuel supply line 91 forignition is interrupted and is not supplied to the lower mold 30anymore.

In STEP S102, the cavity 24 of the upper mold 20, which comes close tothe lower mold 30 at a predetermined distance (for example, 1 to 40 cm),is heated by the gaseous fuel supplied through the air and gaseous fuelline 110 for heating and ignited, for a predetermined time (for example,about 1 to 60 seconds).

In STEP S103, after the supply of air and gaseous fuel is interruptedand flame is extinguished by the interruption of the supply of the airand gaseous fuel, the elevating shaft 82 is elevated by the operation ofthe elevating cylinder 80 and, accordingly, the lower mold 30 is closedby the upper mold 20. As soon as the lower mold 30 is closed by theupper mold 20, molten casting material is supplied through the castingmaterial supply hole 22 of the upper mold 20 from the casting materialfeeder 10.

After the injection of the casting material is completed, STEP S104 isperformed. In STEP S104, after the upper and lower molds 20 and 30 areopened at a predetermined distance (for example, in a range of 1 to 400mm), compressed air is injected toward a formed cast (will be described)through the air and gaseous fuel supply line 110, the supply conduit 31and the discharge holes 34, and cools the formed cast. At this time, thecooling of the formed cast is performed for, for example, 5 to 30minutes.

Additionally, in STEP S105, after the upper and lower molds 20 and 30are completely opened, a formed cast 146 is ejected. With this, theentire injection molding process is completed.

A method for momentarily heating the surface of a mold using the flameof gaseous fuel in accordance with a second embodiment of the presentinvention is described with reference to FIGS. 4a to 4 d. In this case,a core 35 is disposed between the upper and lower molds 20 and 30 as anauxiliary mold for the injection molding of the cast 146.

This system, which can be applied to this method, further comprises onecore 35 disposed between the upper and lower molds 20 and 30, a uppermold supply conduit 21 for supplying mixed gaseous fuel and compressedair, said upper mold supply conduit 21 being formed in the upper mold20, a plurality of upper mold discharge holes 23 for heating and coolingthe core using the mixed gaseous fuel and the compressed air suppliedthrough the upper mold supply conduit 21, a lower mold supply conduit 31for supplying mixed gaseous fuel and compressed air, said lower moldsupply conduit 31 being formed in the lower mold 30, a plurality oflower mold discharge holes 34 for heating and cooling the core 35 usingthe mixed gaseous fuel and the compressed air supplied through the lowermold supply conduit 31, and an air and mixed gaseous fuel supply conduit86 for connecting the air and gaseous fuel mixture and supply unit 90respectively to the upper mold supply conduit 21 and the lower moldsupply conduit 31.

The core 35 is formed to come into tight contact with the upper andlower molds 20 and 30 when the upper and lower molds 20 and 30 areclosed, so that injection pressure is completely transmitted to theupper and lower molds, thus preventing the upper and lower molds frombeing damaged by high injection pressure.

The core 35 has a thickness ranging from 0.1 to 15 mm and is formed tocorrespond to the shape of the cast. The discharge holes 23 and 34 areconstructed in the form of slits, respectively have widths of 0.01 to 5mm and are distributed on the surface of the lower mold 30 to correspondto the shape of the cast.

The method for momentarily heating the surface of a mold in accordancewith the second embodiment is different from the method for momentarilyheating the surface of a mold in accordance with the first embodiment,in that the core 35 is disposed between the upper and lower molds 20 and30, a supply line is connected to the upper mold 20 to supply mixedcompressed air and gaseous fuel, and an ignition unit (not shown)identical to the ignition unit 40 (including the igniter 41, the flamesensor 42 and the high voltage generator 44) mounted to the lower mold30 is preferably mounted to the upper mold 20. Additionally, the core 35is provided with support means for elevating and supporting the core 35.

In STEP S200, the upper mold 20, the core 35 and the lower mold 30 areopened at predetermined distances and the supply of gaseous fuel isprepared. Thereafter, the upper mold 20, the core 35 and the lower mold30 come close to one another at predetermined distances and gaseous fuelis injected to the core 35 from the upper and lower molds 20 and 30 andignited. In more detail, compressed air and gaseous fuel are suppliedfrom the compressed air supply source 136 and the gaseous fuel supplysource 146 through the compressed air supply line 130 and the gaseousfuel supply line 140, enter the air and gaseous fuel supply line 91 forignition and are mixed together while passing through the air andgaseous fuel mixture element 92, and the mixed air and gaseous fuelpasses through the mixed air and gaseous fuel passes through the supplyconduits 21 and 31 of the upper and lower molds 20 and 30, is injectedthrough the discharge holes 23 and 34 and is ignited in the igniter 41of the ignition unit 40 using high voltage current generated by the highvoltage generator 44.

If flame is not sensed by the flame sensor 42 after the ignition isperformed, the supply of air and gaseous fuel is interrupted by theoperation of the solenoid valves 95 and 103.

After the air and gaseous fuel supplied through and mixed in the air andgaseous fuel supply line 91 for ignition are normally injected,compressed air and gaseous fuel are supplied through and mixed in theair and gaseous fuel supply line 110 and are injected through the upperand lower molds 20 and 30. At this time, the supply of the compressedair and gaseous fuel being supplied through the air and gaseous fuelsupply line 91 for ignition is interrupted and is not supplied to theupper and lower molds 20 and 30 anymore. Accordingly, the cavities 24and 38 defined by the upper and lower molds 20 and 30 and the core 35,which come close to one another at predetermined distances (for example,the distances between the upper mold 20 and the core 35 and between thecore 35 and the lower mold 30 are in a range of 1 to 40 cm), are heatedby the gaseous fuel supplied through the air and gaseous fuel line 110for heating and ignited, for a predetermined time period (for example,about 1 to 60 seconds).

In STEP S201, after the supply of air and gaseous fuel supplied from theair and gaseous fuel supply line 110 is interrupted and flame isextinguished by the interruption of the supply of the air and gaseousfuel, the elevating shaft 82 is elevated by the operation of theelevating cylinder 80 and, accordingly, the core 35 and the lower mold30 are closed by the upper mold 20. As soon as the core 35 and the lowermold 30 are closed by the upper mold 20, molten casting material issupplied through the casting material supply hole 22 of the upper mold20 and the casting material supply hole 36 of the core 35 from thecasting material feeder 10.

After the injection of the casting material is completed, STEP S202 isperformed. In STEP S202, after the upper and lower molds 20 and 30 areopened away from the core 35 at predetermined distances (for example, ina range of 1 to 400 mm), compressed air is injected to the core 35 andthe formed cast 146 through the air and gaseous fuel supply line 110,the supply conduits 21 and 31 and discharge holes 23 and 34 and coolsthe core 35 and the formed cast 146. At this time, the cooling of theformed cast 146 is performed for, for example, 5 to 30 minutes.

Additionally, in STEP S203, after the upper and lower molds 20 and 30and the core 35 are completely opened, the formed cast 146 is ejected.With this, the entire injection mold process is completed.

A method for momentarily heating the surface of a mold using the flameof gaseous fuel in accordance with a third embodiment of the presentinvention is described with reference to FIGS. 5a to 5 d. In this case,a plurality of cores are disposed between the upper and lower molds 20and 30 as auxiliary molds for the injection molding of the cast 146.

The cores consist of a first core 35 in contact with the upper mold 20and a second core 37 in contact with the lower mold 30, a castingmaterial supply hole 36 is formed in the first core 35 to correspond tothe casting material supply hole 22 in the upper mold 20, and a formingspace 39 is formed between the first and second cores 35 and 37 to formcasting material supplied through the casting material supply hole 36 ofthe first core 35.

The method for momentarily heating the surface of a mold in accordancewith the second embodiment is different from the method for momentarilyheating the surface of a mold in accordance with the first embodiment,in that a plurality of cores, for example, a first core 35 and a secondcore 37, are disposed between the upper and lower molds 20 and 30, asupply line is connected to the upper mold 20 to supply mixed compressedair and gaseous fuel, and an ignition unit (not shown) identical to theignition unit 40 (including the igniter 41, the flame sensor 42 and thehigh voltage generator 44) mounted to the lower mold 30 is preferablymounted to the upper mold 20. Additionally, the first and second cores35 and 37 are provided with support means for elevating and supportingthe cores 35 and 37.

In STEP S300, the upper mold 20, the first and second cores 35 and 37and the lower mold 30 are opened at predetermined distances and thesupply of gaseous fuel is prepared. Thereafter, the upper mold 20, thefirst and second cores 35 and 37 and the lower mold 30 come close to oneanother at predetermined distances and gaseous fuel is injected to thefirst and second cores 35 and 37 from the upper and lower molds 20 and30 and is ignited. In more detail, compressed air and gaseous fuel aresupplied from the compressed air supply source 136 and the gaseous fuelsupply source 146 through the compressed air supply line 130 and thegaseous fuel supply line 140, enter the air and gaseous fuel supply line91 for ignition and are mixed together while passing through the air andgaseous fuel mixture element 92, and the mixed air and gaseous fuelpasses through the upper and lower molds 20 and 30, is injected throughthe discharge holes 23 and 34 and is ignited in the igniter 41 of theignition unit 40 using high voltage current generated by the highvoltage generator 44.

If flame is not sensed by the flame sensor 42 after the ignition isperformed, the supply of air and gaseous fuel is interrupted by theoperation of the solenoid valves 95 and 103.

After the air and gaseous fuel supplied through and mixed in the air andgaseous fuel supply line 91 for ignition are normally injected,compressed air and gaseous fuel are supplied through and mixed in theair and gaseous fuel supply line 110 and are injected through the supplyconduits 21 and 31 of the upper and lower molds 20 and 30. At this time,the supply of the compressed air and gaseous fuel being supplied throughthe air and gaseous fuel supply line 91 for ignition is interrupted andis not supplied to the upper and lower molds 20 and 30 anymore.Accordingly, the cavities 24 and 38 defined by the upper and lower molds20 and 30 and the first and second cores 35 and 37, which come close toone another at predetermined distances (for example, the distancesbetween the upper mold 20 and the first core 35, between the first core35 and the second core 37 and between the second core 37 and the lowermold 30 are in a range of 1 to 40 cm), are heated by the gaseous fuelsupplied through and injected from the air and gaseous fuel line 110 forheating and ignited, for a predetermined time period (for example, about1 to 60 seconds).

In STEP S301, after the supply of air and gaseous fuel supplied from theair and gaseous fuel supply line 110 is interrupted and flame isextinguished by the interruption of the supply of the air and gaseousfuel, the elevating shaft 82 is elevated by the operation of theelevating cylinder 80 and, accordingly, the first and second cores 35and 37 and the lower mold 30 are closed by the upper mold 20. As soon asthe first and second cores 35 and 37 and the lower mold 30 are closed bythe upper mold 20, molten casting material is supplied through thecasting material supply hole 22 of the upper mold 20 and the castingmaterial supply hole 36 of the first core 35 from the casting materialfeeder 10.

After the injection of the casting material is completed, STEP S302 isperformed. In STEP S302, after the upper and lower molds 20 and 30 areopened away from the first and second cores 35 and 37 at predetermineddistances (for example, in a range of 1 to 400 mm), compressed air isinjected toward the first and second cores 35 and 37 and the formed cast146 through the air and gaseous fuel supply line 110, the supplyconduits 21 and 31 and the discharge holes 23 and 34 and cools the firstand second cores 35 and 37 and the formed cast 146. At this time, thecooling of the formed cast 146 is performed for, for example, 5 to 30minutes.

Additionally, in STEP S303, after heating is performed for a certaintime period, gaseous fuel is injected from the upper and lower molds 20and 30, is ignited and heats the first and second cores 35 and 37. Whilethe first and second cores 35 and 37 are heated, the first and secondcores 35 and 37 are separated and the cast 146 is ejected. With this,all the injection mold process is completed.

As described above, in FIGS. 3a to 3 f, there is depicted the firstembodiment in which no core exists between the upper and lower molds 20and 30. In FIGS. 4a to 4 d, there is depicted the second embodiment inwhich a single core 35 is disposed between the upper and lower molds 20and 30. In FIGS. 5a to 5 d, there is depicted the third embodiment inwhich a plurality of cores 35 and 37 are disposed between the upper andlower mold cores 20 and 30. Of the embodiments, it is preferable that aplurality of cores 35 and 37 are disposed between the upper and lowermold cores 20 and 30.

The cores respectively have thicknesses of 0.1 to 15 mm and are formedto corresponding to the shape of the cast. The discharge holes areconstructed in the form of slits, respectively have widths of 0.01 to 5mm and are distributed on the surface of the lower mold to correspond tothe shape of the cast.

The ignition unit 40 may utilize high voltage current or an electronicspark for igniting mixed air and gaseous fuel, and preferably preparesfor the failure of ignition and an accidental fire after ignition. Suchan ignition unit 40 may be directly mounted on an injection moldingapparatus or separated from the injection molding apparatus. Theignition unit 40 is preferably disposed in the mold and attached to themold. In the ignition mold 40, the length of flames may be adjusted tobe relatively long or relatively short using combustion gas such asgaseous fuel mixed with oxygen or compressed air.

In the air and gaseous fuel mixture and supply unit 90, the gaseous fuelmust be mixed with the oxygen or compressed air for burning the gaseousfuel prior to the supply of the gaseous fuel and the oxygen orcompressed air so as to completely burn the gaseous fuel in a formingspace defined between two molds. Since the danger of explosion occurswhen the gaseous fuel is kept in a state where the gaseous fuel is mixedwith the oxygen or air, the gaseous fuel is mixed with the oxygen or airin the gaseous fuel mixture and supply element 92 for ignition and thegaseous fuel mixture and supply element 111 for heating in the processof supplying the gaseous fuel and the oxygen or air. The gaseous fueland the oxygen or air are supplied to and mixed in the elements 92 and111, and immediately the mixed gaseous fuel and the oxygen or air issupplied to the interior of the lower mold 30. In order to regulate theamount of the gaseous fuel and the amount of the oxygen or air, themanual valves 96, 104, 135 and 145 and the flux regulators 131 and 141are employed. One is selected between the oxygen and the air, dependingupon the material of the molded products. That is, the oxygen isemployed for manufacturing relatively precise injection molding productsof synthetic resin, while the compressed air is employed formanufacturing relatively rough injection molding products. While theoxygen or compressed air is supplied, impurities, such as humidity anddust, must be filtered off through the first filter 132. In the case ofthe gaseous fuel, various impurities must be filtered off through thesecond filter 142 and thereafter be supplied to the lower mold 30.

In the safety unit of the present invention, when it is sensed that thepressure of the gaseous fuel or the oxygen or air supplied through thepneumatic pressure gauge 93 or 112, the fluidic pressure gauge 101 or120 or the pressure switch 134 or 144 is greater or less than apredetermined pressure, the related supply line 91, 110, 130 or 140 isstopped up by the solenoid valve 95, 103, 114, 122, 133 or 143, therebypreventing danger due to abnormal pressure. If the gas detector ismounted to the lower portion of the system of the present invention oron the ceiling of a room where the system of the present invention isinstalled, the supply of the gaseous fuel and oxygen or compressed airis interrupted when the leakage of gas is detected. Additionally, whenthe flame sensor 42 of the ignition unit 40 senses the failure ofignition and an accidental fire, the supply of the gaseous fuel andoxygen or compressed air is interrupted.

The safety unit and the gaseous fuel mixture and supply control 70 forcontrolling the air and gaseous fuel mixture and supply unit 90 allowstheir operating time period, position and numerical value to be set andcontrolled by means of the control panel 150.

EXAMPLE

Wheel caps for automobiles were injection-molded of polycarbonate/ABSalloy resin. The method for momentarily heating the surface of a moldusing the flame of gaseous fuel and system thereof in accordance withthe present invention was applied to the manufacture of the wheel caps.The molding pressure of the system was 405 tons. No resin weld line andno flow mark appeared on the exterior of the molded products.Additionally, pinholes that inevitably appear on the general products ofpolycarbonate/ABS alloy resin did not appear on the products of thisexample. Furthermore, the brilliance, impact strength and thermaldeformation temperature of the products manufactured by the method andsystem were improved as described in table 1 in comparison with theproducts made by the conventional method and system.

TABLE 1 Product made by the Product made by the conventional methodmethod and system of and system the present invention Brilliance (theangle 75 100 of reflection: 60°) Impact strength 52 62 (⅛″, notched ASTMD-256) (Kg.cm/cm) Thermal deformation 123 141 temperature (⅛″, 1.80N/mm² ASTM D-648) (°C.)

As can be seen from the above example, since products ofpolycarbonate/ABS alloy resin having no defect in appearance can bemanufactured in accordance with the present invention, wheel caps ofsuperior quality can be manufactured without coating, thereby reducingits manufacturing cost and improving its quality.

Additionally, in accordance with the present invention, the strength andthermal properties of the products can be improved, and the resin ofhigh strength can be freely formed regardless of its fluidity.

Meanwhile, in accordance with a feature of the present invention, theupper and lower molds 20 and 30 may be heated by an induction heaterthat generates high temperature heat using electricity instead ofgaseous fuel. When the molds 20 and 30 are heated using gaseous fuel,heat is directly applied to the molds 20 and 30; whereas when the molds20 and 30 are heated using an induction heater, electricity flows intothe molds 20 and 30 by the action of induction and heat is generated inthe molds 20 and 30 by the resistance of the molds 20 and 30. When theinduction heater is employed to heat the molds 20 and 30, theconstructions concerning the supply of gaseous fuel are not necessary.However, the constructions concerning the supply of compressed air forcooling the molds 20 and 30 are preferably provided.

That is, in the method and system of the present invention, the upperand lower molds 20 and 30 can be momentarily heated by heating meanssuch as the induction heater.

FIG. 7 is a schematic diagram showing a system for momentarily heatingthe surface of a mold that employs an induction heater and two cores.This system for momentarily heating the surface of a mold comprises acasting material feeder 10 for supplying molten casting material, upperand lower molds 20 and 30 for forming a predetermined shaped cast, aninjection molding control 50 for controlling the upper and lower molds20 and 30, a compressed air supply line 130 for supplying compressedair, one or more cores 35 and 37 disposed between the upper and lowermolds 20 and 30, a voltage generator 73 for generating voltage of apredetermined level, induction heaters 74 and 75 for heating the cores35 and 37 using current applied from the voltage generator 73, theinduction heaters 74 and 75 being mounted on the inner portion of theupper mold 20 and the upper portion of the lower mold 30, a controller72 for controlling the compressed air supply line 130 and the voltagegenerator 73, an interface 60 for interfacing the injection moldingcontrol 50 and the controller 72, and a control panel 150 for visuallydisplaying the control, condition and operation of the components of thesystem.

The system further comprises a plurality of supply conduits 21 and 31and a plurality of discharge holes 23 and 34 in the upper and lowermolds 20 and 30. The supply conduits 21 and 31 are respectivelyconnected to a compressed air supply conduit 87 for supplying compressedair provided by the compressed air supply line 130. The cores 35 and 37respectively have thicknesses of 0.1 to 15 mm and are formed tocorrespond to the shape of the cast. The discharge holes 23 and 34 areconstructed in the form of slits, respectively have widths of 0.01 to 5mm and are distributed on the surfaces of the molds 20 and 30 tocorrespond to the shape of the cast.

When the induction heaters 74 and 75 are employed as heating means, thelower and upper molds 20 and 30 are momentarily heated using currentgenerated by the voltage generator 73 and are cooled by means ofcompressed air of high pressure after injection molding, therebyproducing injection-molded products.

FIG. 8 is a flowchart showing the operation of the system formomentarily heating the surface of a mold that employs the inductionheaters 74 and 75 and the two cores 35 and 37. First of all, in STEPS400, the upper and lower molds 20 and 30 are momentarily heated by theinduction heaters 74 and 75 using current generated by the voltagegenerator 73 after the upper and lower molds 20 and 30 are caused tocome close to each other at a predetermined distance. In STEP S401,molten casting material is injected from the casting material feeder 10and is molded after the heated lower mold 30 is raised to and engagedwith the upper mold 20. In STEP S402, compressed air is supplied from acompressed air supply line 130 to the cores 35 and 37 through acompressed air supply line 87, the supply conduits 21 and 31 and thedischarge holes 23 and 24, and cools the molded product. In STEP S403,the molded product is ejected after the molded product is cooledsufficiently.

A user can select one of the two heating fashions, that is, one heatingfashion using gaseous fuel and the other heating fashion using aninduction heater, depending upon the type or feature of the products tobe injection-molded.

In the meantime, when the induction heaters 74 and 75 are employed, theinjection molding control 50 and interface 60 for controlling thecomponents of the system and a controller 72 for transmitting andreceiving control signals are included in the system. The controller 72includes a control program.

The method and system of the present invention is not limited to theinjection molding of synthetic resin products, but the method and systemcan be applied to reactive injection molding, metallic cast forming andceramic forming and the like.

As described above, the present invention provides a method formomentarily heating the surface of a mold and system thereof, which iscapable of improving the quality of products in appearance, preservingthe physical and thermal properties of resin in the products, increasingthe productivity of the manufacturing process of the products andreducing the manufacturing cost of the products.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A system for momentarily heating the surface of amold, comprising: a casting material feeder for supplying molten castingmaterial; upper and lower molds for forming a predetermined shaped cast;an injection molding control for controlling the upper and lower molds;a compressed air supply line for supplying compressed air; one or morecores disposed between the upper and lower molds; a voltage generatorfor generating voltage of a predetermined level; induction heaters forheating the cores using current applied from the voltage generator, saidinduction heaters being mounted on the inner portion of the upper moldand the upper portion of the lower mold; a controller for controllingthe compressed air supply line and the voltage generator; an interfacefor interfacing the injection molding control and the controller; and acontrol panel for visually displaying the control, condition andoperation of the components of the system.
 2. The system according toclaim 1, further comprising a plurality of supply conduits and aplurality of discharge holes in the upper and lower molds, wherein saidsupply conduits are respectively connected to a compressed air supplyconduit for supplying compressed air provided by the compressed airsupply line.
 3. The system according to claim 2, wherein said coresrespectively have thicknesses of 0.1 to 15 mm and are formed tocorresponding to the shape of the cast, and said discharge holes areconstructed in the form of slits, respectively have widths of 0.01 to 5mm and are distributed on the surfaces of the molds to correspond to theshape of the cast.